debugging slow backup: md5/sha256 confusion

[frhack]

Hi,
I have a proxmox cluster on quite old hardware (80 x Intel(R) Xeon(R) CPU E7- 8870 @ 2.40GHz )
Backup is very slow for machines with large disks.
I suspected a sha256 related issue because I read that vzdump uses sha256 as digest.


Here is the format:
https://git.proxmox.com/?p=pve-qemu.git;a=blob_plain;f=vma_spec.txt;hb=refs/heads/master


But I verified that in reality the vma format uses md5 and not sha256.

So why does proxmox-backup-client benchmark show sha256 performance?